Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Tax credits available for carryforward	$ 4,987	$ 3,042
Net operating loss and other carryforward available	777,263	782,886
Postretirement and pension benefits	47,039	47,122
Allowance for credit losses	269,323	283,303
Depreciation	12,290	12,281
FDIC-assisted transaction	152,665	152,665
Lease liability	50,422	51,811
Unrealized net loss on investment securities	256,764	289,868
Difference in outside basis from pass-through entities	32,800	40,602
Mortgage servicing rights	13,012	13,711
Other temporary differences	38,424	24,937
Total gross deferred tax assets	1,654,989	1,702,228
Deferred tax liabilities:
Intangibles	137,518	135,797
Right of use assets	44,953	46,277
Deferred loan origination fees/cost	4,799	4,037
Loans acquired	22,134	23,353
Other temporary differences	6,581	1,531
Total gross deferred tax liabilities	215,985	210,995
Valuation allowance	534,488	540,196
Net deferred tax asset	904,516	951,037
PR
Deferred tax assets:
Tax credits available for carryforward	261	261
Net operating loss and other carryforward available	121,758	121,742
Postretirement and pension benefits	47,039	47,122
Allowance for credit losses	238,695	250,615
Depreciation	6,033	5,972
FDIC-assisted transaction	152,665	152,665
Lease liability	27,995	28,290
Unrealized net loss on investment securities	235,932	265,955
Difference in outside basis from pass-through entities	32,800	40,602
Mortgage servicing rights	13,012	13,711
Other temporary differences	29,835	17,122
Total gross deferred tax assets	906,025	944,057
Deferred tax liabilities:
Intangibles	82,103	81,174
Right of use assets	25,631	26,015
Deferred loan origination fees/cost	1,804	1,076
Loans acquired	22,134	23,353
Other temporary differences	6,159	1,531
Total gross deferred tax liabilities	137,831	133,149
Valuation allowance	138,016	137,863
Net deferred tax asset	630,178	673,045
US
Deferred tax assets:
Tax credits available for carryforward	4,726	2,781
Net operating loss and other carryforward available	655,505	661,144
Postretirement and pension benefits	0	0
Allowance for credit losses	30,628	32,688
Depreciation	6,257	6,309
FDIC-assisted transaction	0	0
Lease liability	22,427	23,521
Unrealized net loss on investment securities	20,832	23,913
Difference in outside basis from pass-through entities	0	0
Mortgage servicing rights	0	0
Other temporary differences	8,589	7,815
Total gross deferred tax assets	748,964	758,171
Deferred tax liabilities:
Intangibles	55,415	54,623
Right of use assets	19,322	20,262
Deferred loan origination fees/cost	2,995	2,961
Loans acquired	0	0
Other temporary differences	422	0
Total gross deferred tax liabilities	78,154	77,846
Valuation allowance	396,472	402,333
Net deferred tax asset	$ 274,338	$ 277,992